I'm glad he makes the point that Columbus didn't 'discover that the Earth is round'. As he notes, that was a slur invented in the 19th century to depict the bad ol' Catholic Church as anti-science.

In fact, Columbus did what he did because he was relying on a (favorable for his purposes) estimate of the size of the earth that was something like 30% too small, which would put East Asia (which was a known land distance from Europe) within a do-able westward sail. The issue wasn't whether the earth was round or not; it was just that the Muslims held access to the land trade routes to Asia; Columbus' voyages were commercial efforts to do an end-run around the Muslim blockade (as were Vasco da Gama's routes around Africa). The fact that the American continents just happened to be where Columbus thought China was supposed to be was pure dumb luck. . .